Before their flight application, thermal protection materials and hot structures of re-entry configurations must be tested extensively and have to be qualified in ground testing facilities. The arc-heated wind tunnels L2K and L3K are well suited for this purpose as they enable tests in a high enthalpy flow for the duration of a typical entry into the atmosphere.

The purpose of material qualification tests is to verify whether a material is suitable for thermal protection. Investigations on complete thermal protection structures accompany the design stage of a spacecraft which is generally completed with a formal qualification test.

The L2K and L3K facilities offer optimum conditions for the qualification of heat shield components and high temperature sensors for different atmospheres. The emitted light from excited species of a high enthalpy flow field show remarkable differences between the Earth atmosphere and the atmosphere of Mars, which mainly consists of carbon dioxide.

When entering the atmosphere of Mars, apart from thermal structure load, erosion caused by dust particles whirled up high into the atmosphere must also be taken into consideration. Therefore the L2K facility has recently been upgraded for the simulation of particle loaded high enthalpy flows.

Local aerothermodynamic problems arising from thermal protection concepts often cannot be simulated satisfactorily with CFD tools and need to be investigated experimentally. During a post flight analysis of the Japanese HYFLEX mission, for instance, in the frame of an ESA-NASDA/NAL cooperation in the L3K facility the radiation and convective heating including flow phenomena in gaps between thermal protection tiles were investigated systematically.